Conformal wear-resistant bearing assembly

ABSTRACT

A bearing apparatus includes: (a) an inner member comprising rigid material with a first contact surface; (b) an outer member comprising rigid material with a second contact surface; (c) an annular intermediate member between the inner and outer members, and having: (i) a third contact surface including first bearing elements contacting the first contact surface to define a first bearing interface, each first bearing element including a raised central portion flanked beam portions; and (ii) a fourth contact surface including second bearing elements contacting the second contact surface to define a second bearing interface, each second bearing element including a raised central portion flanked by a pair of beam portions; (d) wherein the contact surfaces of each bearing interface are wear-resistant; and (e) wherein the bearing elements are shaped and sized so as to conform in an irregular shape to the at least one contact surface.

BACKGROUND OF THE INVENTION

This invention relates generally to bearings, and more particularly tobearings for use between two components which move relative to eachother.

Numerous types of mechanical assemblies require bearings to providelow-friction contact between two components. Numerous types of bearingsare known, such as plain bushings, hydrodynamic and hydrostaticbearings, and rolling element bearings.

For some applications it is desirable to employ a plain bearing orbushing design using exclusively “hard” materials (e.g. metals orceramics). These materials are suitable for harsh industrialenvironments including for example high temperatures or pressures, orcaustic or corrosive fluids.

Sliding bearing assemblies using two hard elements of conventionaldesign will be, however, subject to rapid wear. First, a bearing havingone hard, rigid element on another will not be perfectly shaped to anominal geometry. Such imperfections will result in points of highstress, thus causing localized wear. Furthermore, two hard elementswould lack the resilient nature of “soft” materials.

BRIEF SUMMARY OF THE INVENTION

These and other shortcomings of the prior art are addressed by thepresent invention, which provides a bearing configuration havingwear-resistant contacting surfaces with conformal properties.

According to one aspect of the invention, a bearing apparatus includes:(a) an inner member comprising a rigid material and defining a firstcontact surface; (b) an outer member comprising a rigid material anddefining a second contact surface; (c) an annular intermediate memberdisposed between the inner and outer members, the intermediate memberhaving: (i) a third contact surface including a plurality of protrudingfirst bearing elements formed therein contacting the first contactsurface of the inner member to define a first bearing interface thattransfers mechanical loads between the inner and intermediate members,while allowing relative translation and/or rotation therebetween,wherein each first bearing element includes a raised central portionflanked by a pair of beam portions; and (ii) a fourth contact surfaceincluding a plurality of protruding second bearing elements formedtherein contacting the second contact surface of the outer member todefine a second bearing interface that transfers mechanical loadsbetween the outer and intermediate members, while allowing relativetranslation and/or rotation therebetween, wherein each second bearingelement includes a raised central portion flanked by a pair of beamportions; (d) wherein the contact surfaces of each bearing interface arewear-resistant; and (e) wherein the bearing elements are shaped andsized so as to deform elastically and conform in an irregular shape tothe at least one contact surface.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may be best understood by reference to the followingdescription taken in conjunction with the accompanying drawing figuresin which:

FIG. 1 is a perspective, partially-exploded view of a bearing assemblyconstructed in accordance with an aspect of the present invention;

FIG. 2 is a cross-sectional view of the bearing assembly of FIG. 1;

FIG. 3 is an enlarged view of a portion of the bearing assembly of FIG.1, in a first condition;

FIG. 4 is an enlarged view of a portion of the bearing assembly of FIG.1, in a second condition;

FIG. 5 is perspective, partially-exploded view of an alternative bearingassembly;

FIG. 6 is a side view of the bearing assembly of FIG. 5;

FIG. 7 is a cross-sectional view of the bearing assembly of FIG. 6;

FIG. 8 is a cross-sectional view of an alternative bearing assembly;

FIG. 9 is an enlarged view of a portion of the bearing assembly of FIG.8;

FIG. 10 is a side view of an inner member, showing a pattern of bearingelements;

FIG. 11 is a side view of an inner member, showing a pattern of bearingelements;

FIG. 12 is a side view of an inner member, showing a pattern of bearingelements;

FIG. 13 is a side view of an inner member, showing a pattern of bearingelements;

FIG. 14 is a side view of an inner member, showing a pattern of bearingelements;

FIG. 15 is a perspective view of an inner member, showing a pattern ofbearing elements;

FIG. 16 is a perspective view of an outer member, showing a pattern ofbearing elements;

FIG. 17 is a side view of an alternative bearing assembly;

FIG. 18 is a cross-sectional view of the bearing assembly of FIG. 17;and

FIG. 19 is a chart showing a wear characteristic of a bearing assemblyof the present invention.

DETAILED DESCRIPTION OF THE INVENTION

In general, the present invention is a bearing assembly for twoconcentric members of a machine or mechanical assembly which can moverelative to each other (e.g. relative rotation or translation). As anexample, the invention could be used between a bore in a housing of anindustrial valve and the shaft or stem of the valve (where the valvestem can rotate and/or translate relative to the housing.) As will beexplained further, the bearing may be a separate component, or parts ofthe bearing may be integral to one or both of the contacting members.Furthermore, the bearing described herein may be used directly betweentwo machine elements, or the assembly described herein (using two memberwith a bearing between them) may be used as a self-contained bearingwithin a larger assembly or device.

The present invention provides a unique bearing element configuration.Generally, the bearing element is flexible enough to allow elasticdeformation and avoid localized load increases, but not so flexible asto risk plastic deformation, cracking and failure. In particular, thebearing element is designed such that the stress levels therein will bebelow the high-cycle fatigue endurance limit. As an example, the bearingelement might be only about 10% to about 20% as stiff as a comparablesolid member. It is also possible to construct the bearing elementgeometry with a variable stiffness, i.e. having a low effective springrate for small deflections and a higher rate as the deflectionsincrease, to avoid failure under sudden heavy loads.

As a general principle, the bearing assembly of the present inventionincludes two mechanical members which require movement therebetween. Abearing is provided, which may be a separate component or integral toone of the members. The bearing includes a wear-resistant contactsurface that bears against the opposing contact surface. The structureof the bearing element is conformal.

The bearing configuration generally includes a protruding bearingelement which is part of a contact surface. The bearing element isconstructed from a rigid material. As used here, the term “rigid” refersto a material which has a high stiffness or modulus of elasticity.Nonlimiting examples of rigid materials having appropriate stiffness forthe purpose of the present invention include stainless steels,cobalt-chrome alloys, titanium, aluminum, and ceramics. By way offurther example, materials such as polymers and elastomers wouldgenerally not be considered “rigid” for the purposes of the presentinvention. Generally, a rigid material should have a modulus ofelasticity of about 0.5×10⁶ psi or greater. The contact surface iswear-resistant. As used herein, the term “wear-resistant” refers to asurface which is resistant to surface material loss when placed underload and has relative motion to another surface. Generally the wearcoefficient of the wear-resistant contact surface should be lower than1.0e-5 mm³/N-m (that is, 1×10⁻⁵ cubic millimeters per Newton-meter).Nonlimiting examples of wear-resistant materials include known coatingssuch as STELLITE, tungsten carbide, titanium nitride, chrome plating,carbon thin films, and/or diamond-like carbon coatings. Such materialsmay be used as a face layer, coating, or film to impart thewear-resistant characteristic to the contact surface of the bearingelement. Such materials are referred to generally herein as“wear-resistant coatings.” Optionally, the contact surface of thebearing element could comprise a substantially thicker face layer of awear-resistant material such as ultra-high molecular weight polyethylene(UHMW-PE) or polyether ether ketone (“PEEK”).

Nominally the two mating contact surfaces (i.e. bearing element andopposing surface) define a contact interface therebetween. In practiceit is impossible to achieve surface profiles completely free of minorimperfections and variations. If the bearing element and the opposingmember were both completely rigid, this would cause high Hertziancontact stresses and rapid wear. Accordingly, an important principle ofthe present invention is that the bearing element and thus theassociated contact surface is conformable to the opposing contactsurface. (The terms “conformable” and “conformal” may be usedinterchangeably herein).

As noted above, it is impossible in practice for either of the contactsurfaces to be perfect surfaces (i.e. a perfect plane, sphere, or othercurve or collection of curves). It is believed that in most cases that asuch as a protrusion from the nominal contact surface of just 0.00127 mm(0.00005 in.), that is, 50 millionths of an inch, or larger, would besufficient to cause fretting corrosion and failure of a metal-on-metaljoint constructed to prior art standards. A defect may include avariance from a nominal surface shape as well as a discontinuity in thecontact surface. Defects may arise through a variety of sources such asmanufacturing, installation, and/or operating loads in the bearingassembly. A bearing having a prior art configuration and made from rigidmaterial cannot conform to such defects through elastic deformation, andhas a tendency to “bridge” across them instead.

Following the principles of the present invention, the bearing elementcan conform to the imperfect opposing contact surface and deflect in anirregular shape. In other words, in addition to any uniform deflectionwhich may be present, the deflected shape of the bearing element caninclude one or more specific locations or portions that are deflectedtowards or away from the nominal free shape to a greater or lesserdegree than the remainder of the bearing element. To achieve thiscontrolled deflection, the bearing element is thin enough to permitbending under working loads, but not so thin as to allow material yieldor fatigue cracking, or to exceed the endurance limit of the material.The deflection is opposed by the elasticity of the bearing element inbending, as well as hoop stresses in the bearing feature. The bearingcould also be designed to allow some controlled plastic deflection. Asused herein, the term “conform” or “conformal” implies a level offlexibility typical of a polymeric or elastomeric material.

The general principles described above are applicable to numerousphysical configurations, several exemplary embodiments of which will bedescribed in more detail below, with reference, to the drawings whereinidentical reference numerals denote the same elements throughout thevarious views.

FIGS. 1-4 illustrate a bearing assembly 100 comprising outer and innermembers 102 and 104. The outer member 102 is an element with a bore 106(a cylindrical bore in this case) defining a first contact surface 108,and the second member 104 is a shaft defining a second contact surface110, passing through the bore 106. In the illustrated example the innermember 104 is hollow, but it could have a solid central cross-section.This example would be representative of the housing of an industrialvalve and the shaft or stem of the valve (where the valve stem canrotate and/or translate relative to the housing.) The inner member 104can rotate about and translate parallel to its own longitudinal centralaxis, relative to the outer member 102.

In the illustrated example the inner member 104 incorporates a pluralityof protruding bearing elements 112. The bearing elements 112 are formedas an annular array of longitudinally-extending ridges withconvex-rounded ends. The bearing elements 112 “protrude” in the sensethat they extend radially outward beyond adjacent portions of the secondcontact surface 110. The second contact surface 110 thus includes bothrecesses and protruding portions, and effectively during use only theprotruding portions would bear against the opposing first contactsurface 108 of the outer member 102. For each bearing element 112, thecross-sectional shape can be conceptualized as including a raisedcentral portion 112A flanked by a pair of beam portions 112B. The beamportions 112B couple the central portion 112A to the remainder of thesecond contact surface 110. The term “beam portion” refers to astructure which is loaded in bending, similar to a conventionalstructural beam. This cross-sectional configuration is common to all ofthe bearing elements described herein.

The bearing elements 112 are constructed from a rigid material asdescribed above, and the second contact surface 110 is wear-resistant asdescribed above. In the configuration shown in FIG. 3, the portion ofthe second contact surface 110 at the peaks of the bearing elements 112is convex. The cross-sectional profile of the bearing elements 112 maybe flat or curved as necessary to suit a particular application. Whenviewed in half-sectional profile, the bearing elements 112 are arcuate,such that contact between them and the outer member 102 tends to causebending deflection of the bearing elements 112.

The outer member 102 is also made from a rigid material, and the firstcontact surface 108 is wear-resistant as described above. Whenassembled, the contact surfaces 108 and 110 bear directly against eachother so as to transfer mechanical loads between the outer and innermembers 102 and 104 while allowing relative sliding motion between thecontact surfaces (and thus, relative sliding or rotation between thefirst and second members 102 and 104). The contact surfaces 108 and 110are wear-resistant as described above.

The bearing elements 112 may be sized relative to the outer member 102such that there is some degree of static deflection or “preload” in thebearing elements 112 when the outer and inner members 102 and 104 arestatically assembled, or there may be some radial clearance between thetwo when statically assembled.

In practice it is impossible to achieve surface profiles completely freeof minor imperfections and variations. If the bearing elements 112 andthe outer member 102 were both completely rigid, this would cause highHertzian contact stresses and rapid wear. Accordingly, an importantfeature of the illustrated assembly 100 is that the bearing elements 112and thus the second contact surface 110 is conformable to the opposingfirst contact surface 108, as described above. In the case were theinner member 104 were to have a solid cross-section, the bearingelements 112 would be incorporated as part of a separate sleevesurrounding the solid inner core, so as to provide the neededflexibility for the bearing elements 112.

FIG. 3 shows a cross-sectional view of one of the bearing elements 112in an initial condition. It can be seen that the second contact surface110 bears against the first contact surface 108 of the outer member 102,creating a contact region or band of first width “W1”. FIG. 4 shows thebearing element 112 in a position after wear (or under a loadedcondition), resulting in a substantially increased contact surface areawidth “W2” between the contact surfaces 108 and 110.). This increasescontact area and therefore decreases contact stress for a given load. Asdescribed above, the bearing element 112 can conform to the imperfectcontact surface 108 and deflect in an irregular shape. The bearingelement 112 is sized to achieve this controlled deflection as describedabove.

FIGS. 5-7 illustrate an alternative assembly 200 which is similar inconstruction to the bearing assembly 100 described above and includesouter and inner members 202 and 204. The outer member 202 is an elementwith a bore 206 defining a first contact surface 208, and the innermember 204 is a shaft defining a second contact surface 210, passingthrough the bore 206. In the illustrated example the inner member 204 ishollow, but it could have a solid central cross-section. The innermember 204 can rotate about and translate parallel to its ownlongitudinal central axis, relative to the outer member 202.

The inner member 204 incorporates a plurality of protruding bearingelements 212. The bearing elements 212 are formed in a longitudinalarray of circumferentially-extending ridges. The bearing elements 212are constructed from a rigid material as described above, and the secondcontact surface 210 is wear-resistant as described above. In theillustrated configuration, the portion of the second contact surface 210at the peaks of the bearing elements 212 is convex. The cross-sectionalprofile of the bearing elements 212 may be flat or curved as necessaryto suit a particular application. When viewed in half-sectional profile,the bearing elements 112 are arcuate, such that contact between them andthe outer member 102 tends to cause bending deflection of the bearingelements 212.

The outer member 202 is also made from a rigid material, and the firstcontact surface 208 is wear-resistant as described above. The contactsurfaces 208 and 210 are wear-resistant as described above. Whenassembled, the contact surfaces 208 and 210 bear directly against eachother so as to transfer mechanical loads between the outer and innermembers 202 and 204 while allowing relative sliding motion between thecontact surfaces (and thus, relative sliding or rotation between thefirst and second members 202 and 204).

The bearing elements 212 (and thus the second contact surface 210) areconformable to the opposing first contact surface 208, as describedabove. In the case were the inner member 204 were to have a solidcross-section, the bearing elements 212 would be incorporated as part ofa separate sleeve surrounding the solid inner core, so as to provide theneeded flexibility for the bearing elements 212.

The bearing elements 212 may be sized relative to the outer member 202such that there is some degree of static deflection or “preload” in thebearing elements 212 when the outer and inner members 202 and 204 arestatically assembled, or there may be some radial clearance between thetwo when statically assembled.

FIGS. 8 and 9 show an inner member 204′ illustrating the concept thatthe wall thickness of the inner member 204′ can be selectively varied totailor the characteristics of bearing elements 212′ to a particularapplication.

FIGS. 10-14 depict several variants of inner members similar in designto the inner member 104 described above, but having the bearing elementarranged in as arrays of individual “islands”. In plan view the bearingelements may be square, circular, rectangular, or oval, as desired toadapt them to various applications.

FIG. 15 illustrates an alternative inner member 304 generally similar inconstruction to the inner member 104 described above. It incorporates aplurality of protruding bearing elements 312. The bearing elements 312are formed as an annular array of ridges with convex-rounded ends. Eachbearing element 312 has an elongated “Z”-shape with axially-extendingend segments 314 circumferentially offset from each other andinterconnected by an oblique central segment 316. The bearing elements312 are constructed from a rigid material as described above with acontact surface that is wear-resistant as described above, and areconformal as described above. This configuration of bearing elements 312may be used when the expected motion is a combination of translation androtation.

FIG. 16 illustrates an alternative outer member 402 generally similar inconstruction to the inner member 202 described above. It incorporates aplurality of bearing elements 412 that protrude inward. Thisconfiguration would be used in conjunction with an inner member (notshown) having a plain outer contact surface without bearing elements. Asillustrated the bearing elements 412 are formed as an array ofindividual “islands”, but any of the configurations described abovecould be used. The bearing elements 412 are constructed from a rigidmaterial as described above with a contact surface is wear-resistant asdescribed above, and are conformal as described above.

FIGS. 17 and 18 illustrate a bearing assembly 500 comprising outer andinner members 502 and 504, with an intermediate member 506 disposedtherebetween. The outer member 502 is an element with a bore 511 (acylindrical bore in this case) defining a first contact surface 508, andthe inner member 504 is a shaft defining a second contact surface 510.In the illustrated example the inner member 504 is hollow, but it couldhave a solid central cross-section. The inner member 504 can rotateabout and translate parallel to its own longitudinal central axis,relative to the outer member 502. The outer and inner members 502 and504 are made from rigid materials, and their contact surfaces arewear-resistant as described above.

The intermediate member 506 is annular and has opposed third and fourthcontact surfaces 512 and 514, respectively. The third contact surface512 bears against the second contact surface 510, and the fourth contactsurface 514 bears against the first contact surface 508. Theintermediate member incorporates a plurality of inner bearing elements516 protruding from the third contact surface 512, and a plurality ofouter bearing elements 518 protruding from the fourth contact surface514. In the example shown in FIG. 18, the inner and outer bearingelements 516 and 518 are formed as an annular array oflongitudinally-extending ridges with convex-rounded ends; however any ofthe configurations illustrated and described herein may be usedtherefor, for example the circumferential or individual bearing elementconfigurations discussed above. As shown in FIG. 18, the backside ofeach of the inner bearing element 516 may form the recessed portion or“valley” between adjacent outer bearing elements 518, and vice-versa.The third and fourth contact surfaces 512 and 514 thus include bothrecesses and protruding portions, and effectively during use only theprotruding portions would bear against the opposing first contactsurface 508 of the outer member 502 and the second contact surface 510of the inner member 504, respectively.

The intermediate member 506 is constructed from a rigid material asdescribed above, and its contact surfaces 512 and 514 are wear-resistantas described above. The contact surfaces of each bearing interface ofthe assembly 500 (that is, each location where two contact surfacesmeet) are wear-resistant. The cross-sectional profile of the bearingelements 516 and 518 may be flat or curved as necessary to suit aparticular application. When viewed in half-sectional profile, thebearing elements 516 and 518 are arcuate, such that contact between themand the inner and outer members 504 and 502 tends to cause bendingdeflection of the bearing elements 516 and 518. The bearing elements 516and 518 are conformal as described above.

Optionally, any of the bearing assemblies described above may bedesigned in conjunction with the opposing contact surface to create awear characteristic that is constantly diminishing (similar to anasymptotic characteristic). For example, considering the bearingelements 112 (shown generally in FIG. 2), in FIG. 3 the initialassembled condition is shown. When assembled and placed under load, theinterface (contact region) between each of the contact surfaces 108 and110 will have a characteristic width denoted “W1”. The initialdimensions of the bearing element 112 are selected such that, even usingwear-resistant surfaces or coatings, some wear takes place during aninitial wear-in period of movement cycles. in this situation, thewear-resistant surface may function as a sacrificial element to somedegree. For example, some of the initial thickness of a coating or thinfilm could wear away. As a result, the contact band width increasesduring the initial wear-in period to a second, larger value “W2” (seenin FIG. 4). This increases contact area and therefore decreases contactstress for a given load. After the initial wear-in period (which couldoccur before the assembly is placed into its end use), the contact bandreaches a post wear-in width at which the contact stress is below aselected limit, below which the rate of wear in the contacting surfacesapproaches a very low number or zero, consistent with a long life of thebearing assembly 100. FIG. 19 illustrates this wear characteristic, withthe limit “L” depicted as a horizontal line.

It is noted that the increase in contact band or contact region area(e.g. as shown in FIGS. 3 to 4) can occur as a result of changes inloading or from initial wear-in, or from a combination of both loadingand wear-in.

The configuration of the bearing element 112 is important in developingthe constantly diminishing wear characteristics described above. Inparticular, the bearing element 112 may be sized and shaped so thatdeflections of the contact surface 110 under varying loads is alwaysessentially normal to its tangent point on the opposing contact surface108, as the bearing element 112 is loaded and unloaded. This ensuresthat the centroid of the contact region on the bearing element 112remains constant.

As noted above, known coatings such as STELLITE, tungsten carbide,titanium nitride, chrome plating, carbon thin films, and/or diamond-likecarbon coatings may be used to impart wear resistance or augment thewear resistance of any of the contact surfaces described above. To thesame end, it may be desirable to surface treat either or both interfacesof any of the above-described contact surfaces with a laser, shot peen,burnishing, or water shock process, to impart residual compressivestresses and reduce wear. The benefit could be as much from surfaceannealing and microstructure and microfracture elimination as smoothingitself.

The foregoing has described a bearing assembly with wear-resistantproperties and conformable geometries. While specific embodiments of thepresent invention have been described, it will be apparent to thoseskilled in the art that various modifications thereto can be madewithout departing from the spirit and scope of the invention.Accordingly, the foregoing description of the preferred embodiment ofthe invention and the best mode for practicing the invention areprovided for the purpose of illustration only and not for the purpose oflimitation.

What is claimed is:
 1. A bearing apparatus, comprising: (a) an innermember comprising a rigid material and defining a first contact surface;(b) an outer member comprising a rigid material and defining a secondcontact surface; (c) an annular intermediate member disposed between theinner and outer members, the intermediate member having: (i) a thirdcontact surface including a plurality of protruding first bearingelements formed therein contacting the first contact surface of theinner member to define a first bearing interface that transfersmechanical loads between the inner and intermediate members, whileallowing relative translation and/or rotation therebetween, wherein eachfirst bearing element includes a raised central portion flanked by apair of beam portions; and (ii) a fourth contact surface including aplurality of protruding second bearing elements formed thereincontacting the second contact surface of the outer member to define asecond bearing interface that transfers mechanical loads between theouter and intermediate members, while allowing relative translationand/or rotation therebetween, wherein each second bearing elementincludes a raised central portion flanked by a pair of beam portions;(d) wherein the contact surfaces of each bearing interface arewear-resistant; and (e) wherein the bearing elements are shaped andsized so as to deform elastically and conform in an irregular shape tothe at least one contact surface.
 2. The apparatus of claim 1 whereinthe protruding bearing elements comprise longitudinally-extendingridges.
 3. The apparatus of claim 1 wherein the protruding bearingelements comprise circumferentially-extending ridges.
 4. The apparatusof claim 1 wherein the protruding bearing elements comprise an array ofindividual elements.
 5. The apparatus of claim 1, wherein all of thecontact surfaces are ceramic, metallic, or a combination thereof.
 6. Theapparatus of claim 1, wherein the bearing elements are sized so as topermit elastic deflection of the bearing elements while limitingstresses in the bearing elements to less than the endurance limit of thematerial, when a predetermined load is applied to the apparatus.
 7. Theapparatus of claim 1 wherein the bearing elements and the contactsurfaces are configured to produce an asymptotic wear characteristicwhen in use.
 8. The apparatus of claim 1 wherein the bearing elementsare configured to produce a varying area contact region in response tochanges in load acting on the apparatus.
 9. The apparatus of claim 1wherein the bearing elements are made from a material more rigid thanboth elastomers and polymers.
 10. The apparatus of claim 1 wherein atleast one of the first member, the second member, and the bearingelements has a wear-resistant coating disposed thereon.
 11. Theapparatus of claim 1 wherein the bearing elements are configured todefine a contact region with one of the first and second contactsurfaces, such that a centroid of the contact region remains stationaryin response to changes in pressure on the apparatus.